Ten thousand years ago, Emperor Shaohao, the Last Emperor of Pandaria, used the power of these sacred waters to spare Pandaria from the devastation of the Sundering that destroyed the rest of the world.
From the Book of Burdens, Epilogue:
"At the dusk of the final day, the sky was bathed in green fire, and the very ground trembled in terror. But the Emperor was not afraid. His mind was clear of any doubt or despair. He feasted and he sang as the sky tore open."
"Seeing fear and doubt in his subject's eyes, Emperor Shaohao delivered a proclamation: That one should live each day to its fullest, and sleep each night with the peace of a mind unburdened."
Legend tells that he ascended to the Terrace of Endless Spring, there to separate Pandaria from the rest of the world. But try as he might, he was unable; the ground trembled, but did not move. Soon, he began to doubt, and the Sha of Doubt began to emerge from the east. He began to fear, and the Sha of Fear began ripping out of its shackles to the west. Desperately, he called out to the Jade Serpent for help.
The Jade Serpent circled the Vale, and spoke to the beleaguered Emperor. "Pandaria is more than just the Pandaren Empire," she told Shaohao. "Your enemies to the west are as much a part of this land as your empire behind the wall."
Seeing that all things were connected in an eternal whole, and that his beloved land was more than just the Pandaren Empire, Shaohao at last understood. His staff clattered to the floor as his spirit became one with the land. When the world tore itself apart, Pandaria drifted quietly into the ocean. And as the Emperor's robes fluttered empty to the ground, the land became enveloped in impenetrable mists, hidden away from the rest of the world.